Layered Sphere Catalyst Formulations for Selective Hydrogenation Performance

ABSTRACT

A catalyst for selective hydrogenation of hydrocarbons is presented. The catalyst selectively hydrogenates acetylenes and diolefins to increase the monoolefins in a product stream. The catalyst includes a layered structure with an inert inner core and an outer layer bonded to the inner core, where the outer layer is a metal oxide and has at least two metals deposited on the outer layer.

FIELD OF THE INVENTION

The invention relates to the selective hydrogenation of hydrocarbons.More specifically, the invention relates to of a catalyst to selectivelyhydrogenate C3-C11 diolefins and acetylenes in a hydrocarbon mixture toone or more respective C3-C11 monoolefins.

BACKGROUND OF THE INVENTION

Hydrocarbon stream feeds like pyrolysis gas feeds can have diene valuesranging from 1-120 and diolefin weight percentages in such streams canrange from 0.5 weight percent to 50 weight percent or above. Under anoxygen atmosphere diolefins are unstable. Diolefins present a challengefor processes involving catalysts because the diolefins are veryreactive and polymerize even under hydrogen atmospheres at hightemperatures forming gum. Because of the reactivity of diolefinscatalysts that have poor activity are restricted in cycle length andhave a propensity for polymerization because of the requirement for hightemperatures. It is generally accepted at temperatures about 170° C.(338° F.) excess polymerization causes pressure drops across a catalyticreactor. These problems are generally worse if the catalyst comprises aporous active base such as gamma or theta alumina where polymerizationof diolefins can cause swelling of the porous catalyst and can damagethe structure of the catalyst.

In situations where the catalyst is an active catalyst there is atendency for the active catalysts to convert diolefins and acetylenes aswell as the monoolefins rapidly and often more selectively to theircorresponding paraffins and naphthenes causing excess heat generation.Again, these conditions tend to favor gum formation and this isparticularly so in a commercial application where a fixed bed adiabaticreactor is subjected to high temperature rises. The reactor's practicaloperating window is limited because of the pressure drop problems.

The current industrial practice for selectively hydrogenating diolefinsor unsaturated hydrocarbon fractions is based on the use of sulfidednickel catalysts operating at moderately high temperatures ofapproximately 185° C. (365° F.). Sulfur loss from the catalyst to theproduct occurs and sulfur must be replenished to keep the catalystactive and operating optimally. Furthermore, once the sulfur is lostinto the product, in some instances the sulfur must also be removed fromthe product and this adds another level of processing.

Other types of selective hydrogenation processes are also known, such asthat described in JP54157507A. JP 54157507A describes the use of apalladium catalyst on an alumina support to selectively hydrogenateacetylene and methyl acetylene(alkynes) that are present in olefinfractions obtained in petrochemical processes. The catalyst described inJP54157507A comprises a thin alumina coating over an alpha aluminacarrier of spherical or cylindrical shape and being around 1-20 mm insize, length and diameter. The alumina precursor, which can be aluminumnitrate, aluminum chloride, aluminum hydroxide and the like, is coatedonto the alpha alumina carrier and then the coated alpha alumina carrierand alumina precursor is heat treated at between 400° C. (752° F.) to700° C. (1292° F.) to create a thin alumina coating over the alphaalumina carrier. A palladium compound such as palladium chloride,palladium nitrate, and the like is dissolved in a suitable solvent, andthen applied to the alumina coating to give effectively an enrichedsurface coating containing palladium. JP54157507A describes the use ofthe resulting catalyst in the selective hydrogenation of acetylene in acomposition comprising ethylene.

US 2003/0036476 A1 describes a coated catalyst having a core and a shellsurrounding the core, the core is made up of an inert support material.The shell is made up of a porous support substance, and the shell isphysically attached to the core. A catalytically active metal selectedfrom the group consisting of the metals of the 10th and 11th groups ofthe Periodic Table of the Elements is present in finely divided form inthe shell. The coated catalyst is described as being suitable for theselective reduction of unsaturated hydrocarbons, specifically lowerC2-C4 unsaturated hydrocarbons.

U.S. Pat. No. 6,177,381 B1, which is incorporated by reference in itsentirety, describes a layered catalyst composition showing improveddurability and selectivity for dehydrogenating hydrocarbons, a processfor preparing the catalyst and processes for using the composition. Thecatalyst composition comprises an inner core such as alpha-alumina, andan outer layer bonded to the inner core composed of an outernon-refractory inorganic oxide such as gamma-alumina. The outer layerhas uniformly dispersed thereon a platinum group metal such as platinumand a promoter metal such as tin. The composition also contains amodifier metal such as lithium. The catalyst composition is prepared byusing an organic binding agent such as polyvinyl alcohol which increasesthe bond between the outer layer and the inner core. The catalystcomposition is described as also being suitable for use indehydrogenation and hydrogenation processes. Likewise, U.S. Pat. No.6,280,608 B1 also describes a layered catalyst suitable for use indehydrogenation and hydrogenation processes, while U.S. Pat. No.6,486,370 B1 is directed to a layered catalyst suitable for use indehydrogenation processes.

US 2006/0266673 A1 and US 2006/0270865 A1 describe a similar layeredcatalyst, but with an additional fibrous component in the outer layer.The fiber-containing layered catalyst is described as being suitable foruse in dehydrogenation and hydrogenation processes including selectivehydrogenation of dienes and trienes.

Improvements in selective hydrogenation is very important for reducingwaste and recycle, thereby saving energy and material in the process.Improvements have a significant economic impact on the production ofolefins.

SUMMARY OF THE INVENTION

The present invention provides for a new catalyst that improves theselective hydrogenation of diolefins and acetylenes. The catalystcomprises a layered structure, having an inner core made of an inertmaterial, and an outer layer bonded to the inner core. The outer layeris a metal oxide selected from one or more of gamma alumina, deltaalumina, eta alumina, theta alumina, silica-alumina, zeolites,nonzeolitic molecular sieves, titania and zirconia. The catalyst furtherincludes a first metal deposited on the outer layer. The first metal isdeposited on the outer layer in an amount such that the atomic ratio ofthe first metal to the aluminum in the outer layer is between 0.0001 and0.1. The catalyst further includes a second metal deposited on the outerlayer. The first metal is one or more metals selected from IUPAC Group8-10 metals, and the second metal is one or more metals selected fromIUPAC Group 11-17 metals.

In a specific embodiment, the catalyst comprises a composition such thatthe atomic ratio of the second metal to the first metal is less than 6.

Additional objects, embodiments and details of this invention can beobtained from the following drawings and detailed description of theinvention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plot of the palladium to aluminum atomic ratio profile inthe outer layer as a function of distance in nanometers from the surfaceof the catalyst;

FIG. 2 is a plot of the copper to palladium atomic ratio profile in theouter layer as a function of distance in nanometers from the surface ofthe catalyst;

FIG. 3 is a plot of the activity for methyl acetylene and propadieneconversion to propylene versus LHSV;

FIG. 4 is a plot of the selectivity for propylene recovery in percentversus methyl acetylene and propadiene conversion;

FIG. 5 is a plot of the palladium to aluminum layer profiles forpalladium only catalysts;

FIG. 6 is a plot of the activity for methyl acetylene and propadieneconversion to propylene versus LHSV;

FIG. 7 is a plot of the selectivity for propylene recovery in percentversus methyl acetylene and propadiene conversion; and

FIG. 8 is a plot of the organic and H2S sulfur recoveries.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a layered catalyst, and the use of thecatalyst to selectively hydrogenate C3-C11 diolefins and acetylenes toC3-C11 monoolefins, which helps to mitigate some of the above mentionedlimitations. The layered catalyst composition comprises an IUPAC Group8-10 metal and an IUPAC Group 11-17 metal on a layered compositionsupport. The support comprises an inner core of an inorganic oxide,which is preferably a refractory inorganic oxide, such as, withoutlimitation, cordierite, and an outer layer of a non-refractory inorganicoxide, such as, without limitation, gamma alumina.

The product and process disclosed herein has been developed to enableone to selectively hydrogenate C3-C11 diolefins and acetylenes to C3-C11monoolefins at relatively high space velocities using a layered catalystthat eliminates the need to use a sulfided nickel catalyst. Thiseliminates the need for associated sulfur addition due to loss of sulfurfrom the catalyst, and in some instances the subsequent removal ofsulfur from the product as sulfur loss from the catalyst is lost intothe product.

In particular, the catalyst comprises a layered structure having aninner core made of an inert material, and an outer layer bonded to theinner core. The outer layer comprises a metal oxide selected from gammaalumina, delta alumina, eta alumina, theta alumina, silica-alumina,zeolites, nonzeolitic molecular sieves, titania, zirconia, and mixturesof these oxides. The outer layer includes a first metal deposited on theouter layer where the first metal is one or more metals selected fromIUPAC Group 8-10 metals. The outer layer further includes a second metaldeposited on the outer layer where the second metal is one or moremetals selected from IUPAC Group 11-17 metals, and where the first andsecond metals are deposited in amounts such that the atomic ratio of thefirst metal to the aluminum in the outer layer is between 0.0001 and0.1. It is preferred that the atomic ratio of the first metal to thealuminum in the outer layer is between 0.001 and 0.005.

The layered structure of the catalyst comprises an inner core whereinthe inner core is a solid material comprising one or more of thefollowing materials: cordierite, mullite, olivine, zirconia, spinel,kyanite, aluminas, silicas, aluminates, silicates, titania, nitrides,carbides, borosilicates, boria, aluminum silicates, magnesia, fosterite,kaolin, kaolinite, montmorillonite, saponite, bentonite, clays that havelittle or low acidic activity, gamma alumina, delta alumina, etaalumina, and theta alumina. The inner core has an effective diameter ofbetween 0.05 mm and 10 mm. By effective diameter is meant, fornon-spherical shapes, the diameter that the shaped particle would haveif it were molded into a sphere. In a preferred embodiment, the driedshaped particles are substantially spherical in shape. The outer layeris deposited on and bonded to the inner core to an effective thicknessbetween 1 and 200 micrometers. A preferred outer layer thickness isbetween 20 and 70 micrometers.

In one embodiment, the outer layer comprises alumina. Preferred aluminasinclude gamma-alumina, theta-alumina, and silica-alumina. In referringsilica-alumina, it should be noted that the term silica-alumina does notmean a physical mixture of silica and alumina but means an amorphousmaterial that has been cogelled or coprecipitated.

In a preferred embodiment, the first metal is either palladium (Pd) orplatinum (Pt), and the second metal is copper (Cu), silver (Ag), gold(Au), tin (Sn), germanium (Ge), lead (Pb), or a mixture of the secondmetals. The atomic ratio of the metals in the outer, or active, layer isimportant for the performance of the catalyst. If is preferred that theatomic ratio of the second metal to the first metal be less than 6, witha more preferred atomic ratio of less than 3, and a most preferred ratioof less than 1.5.

In one embodiment, the catalyst further includes a third metal depositedon the outer layer. The third metal is one or more metals selected fromIUPAC Group 1-2 metals. In a preferred embodiment, the third metal iseither potassium (K), lithium (Li), or a mixture of potassium andlithium.

In another embodiment, the catalyst further comprises a modifier metaldeposited on the outer layer. The modifier metal is one or more metalsselected from IUPAC Group 6-7 metals. Preferred modifier metals includemolybdenum (Mo), tungsten (W), or rhenium (Re).

An example catalyst of the present invention is one that is preferred tocomprise a layered structure having an inner core of an inert materialand an outer layer bonded to the inner core with the outer layercomprising an alumina. The inner core is formed to have an effectivediameter between 0.05 mm and 10 mm, with the outer layer having aneffective thickness between 1 and 200 micrometers. The catalyst furthercomprises palladium deposited on the outer layer and copper deposited onthe outer layer. The palladium is deposited in an amount such that thepalladium to aluminum atomic ratio is between 0.001 and 0.005. Thecopper is deposited in an amount such that the atomic ratio of copper topalladium is less than 6, and preferably less than 1.5.

The catalyst of the present invention is for the selective hydrogenationof hydrocarbon streams having diolefins and/or acetylenes. Thehydrocarbons are in the C3 to C11 range, and the hydrogenation processconverts the diolefins and acetylenes to monoolefins in the C3 to C11range. The hydrocarbon stream is contacted with the layered catalyst asdescribed above at selected hydrogenation conditions in a hydrogenationreactor.

Selective hydrogenation conditions include operation of thehydrogenation reactor at a temperature between 30° C. and 300° C. Theoperation includes running the process under a hydrogen atmosphere, or apartial hydrogen atmosphere with an inert diluent. The reaction iscarried out at a hydrogen to diolefin and acetylene molar ratio between1:1 and 10:1, or with a hydrogen to total liquid feed molar ratiobetween 0.1:1 and 20:1. The selective hydrogenation furthermore can takeplace in a complete liquid or gas phase or in a mixture of the twophases. The temperature and pressure can be adjusted to operate betweenbubble and dew points of the reactive mixture.

The process converts between 30% and 100% of the diolefins andacetylenes to monoolefins. In a preferred operation, the processconverts light ends of the hydrocarbon stream, in particular, the C3components, or methyl acetylene and propadiene. The methyl acetylene andpropadiene are converted to propylene for enhancing propylene productionfrom processes that generate methyl acetylene and propadiene. Thediolefin conversion can be completed in one reactor vessel or inmultiple vessels that can be connected in series or in parallel. Thediolefin content can be at least 5 ppm by wt.

Experiments:

The layered sphere catalyst was studied for performance in improving theselective hydrogenation of lower molecular weight hydrocarbons, and inparticular acetylenes and dienes. The effects studied include theeffects of the atomic ratios of the first metal, palladium, to thealuminum, and the atomic ratios of the first metal, palladium, to thesecond metal, copper, in the active layer on the catalyst performance.These are mainly characterized by XPS profiling. The experiments wereperformed using methyl acetylene (MA) and propadiene (PD), or MAPD, overthe catalyst for selective hydrogenation to propylene.

From the experiments, a Pd:Al ratio between 0.001 and 0.005 in theactive layer appeared to give optimum performance for the palladiummetal. This ratio can change for a metal oxide other than alumina. Thesecond metal to first metal ratio was found to give the best performancewhen the atomic ratio was less then 3 and preferably less than 1.5. Thefirst metal in the experiments was palladium, and the second metal usedwas copper, silver, or gold.

These formulations were robust in that they were recoverable fromorganic upsets, or from H₂S sulfur upsets.

Several catalysts were made and used with Pd and Cu in the outer, oractive, layer. A first catalyst, Catalyst A, comprised a layered spherewith an inner core of cordierite with a 3 mm diameter, and a 50micrometer outer layer of γ-alumina (Al₂O₃). The metals deposited on theouter layer were 0.02 wt % Pd, 0.038 wt % Cu, and 0.33 wt % K on thebulk basis. The theoretical CtL/Pd molar ratio is 3 based on the bulkICP, and the theoretical Pd/Al atomic ratio in the layer is 0.001. Thecatalyst was prepared with long evaporation procedure with acid.

A second catalyst, Catalyst B, comprised the same makeup as catalyst A,except the preparation was with a short evaporation time.

A third catalyst, Catalyst C, comprised a layered sphere with an innercore of cordierite with a 3 mm diameter, and a 25 micrometer outer layerof γ-alumina (Al₂O₃). The metals deposited on the outer layer were 0.02wt % Pd, 0.012 wt % Cu, and 0.33 wt % K on the bulk basis. Thetheoretical Cu/Pd molar ratio is 1 based on the bulk ICP, and thetheoretical Pd/Al atomic ratio in the layer is 0.002. The catalyst wasprepared with long evaporation procedure with acid.

The theoretical calculation of Pd:Al atomic ratio for a layered spherecatalyst having a 3 mm core and a 50 micrometer outer layer ofγ-alumina, and with a 200 wt. ppm Pd loading comprises the followingcalculation. On a 100 gm catalyst basis, the layer weight of 10.2 gramsfor 100 grams of catalyst as measured, the moles ofPd=0.02/106.4=0.000188; and the grams of Al=10.2*(2*26.98)/101.06=5.4,which translates to moles of Al=5.4/26.98=2. The mole, or atomic, ratioof Pd:Al=0.00094 or approximately 0.001.

For a zirconia (ZrO₂) case, with a layered sphere catalyst having a 3 mmcore and a 25 micrometer zirconia layer base, the wt. % zirconia layeris 12 wt %. On a 100 gm catalyst basis, the grams ofZr=12*91.22/(91.22+2*16)=8.8836; and the moles ofZr=8.8836/91.22=0.9738. For the same Pd loading of 0.02 wt %, the Pd:Zratomic ratio=(moles of Pd/moles of Zr)=0.000188/0.09738=0.00193, orapproximately 0.002. This is almost twice the Pd:Al ratio calculationabove.

The distribution of Pd on the outer layer is shown in FIG. 1 by thePd:Al ratio profiles taken with XPS sputtering. Catalyst A, as expected,shows a measured Pd:Al ratio of between 0.001 and 0.002. Catalyst B hastwice the ratio of Catalyst A, showing more surface enrichment of Pd inthe outer layer. Catalyst C had a layer thickness set at 25 micrometers,and as a result Catalyst B and Catalyst C have similar Pd:Al ratios, butCatalyst C has a more uniform Pd profile due to the long evaporationprocedure.

The distribution of the second metal to first metal, or Cu:Pd ratios, isshown in FIG. 2. Catalyst A has a high Cu:Pd ratio of around 3, asintended. Catalyst B, due to surface enrichment of the Pd has a Cu:Pdratio of around 1. Catalyst C, as designed after Catalyst B, achievesthe same Cu:Pd ratio of around 1, but with a more uniform profile.

The performance of these three catalysts is compared for the selectivehydrogenation of MAPD and is shown in FIGS. 3 and 4. The catalysts allhave nominally the same bulk Pd composition. The feed composition had1300 wt. ppm MA and 300 wt. ppm PD, 65/35 C3/C3=. The reactionconditions were 3550 kPa (500 psig) with a hydrogen to MAPD molar ratioof 1.2. The catalyst bed temperature was 40° C. The results shown inFIG. 3 indicate that Catalyst B is more active than Catalyst A, and thatCatalyst C is even more active than Catalyst B. The propylene recoveryis shown as a function of MAPD conversion in FIG. 4. Catalysts A and Bhave similar selectivities at the higher conversion, while Catalyst Chas the best selectivity at the higher conversion. The differences,although nominally the same bulk conditions, point to the importance ofthe ratios of the metals deposited on the outer layer.

A second set of catalysts were formed and tested. These catalystscomprised a palladium on alumina formulation only for differing Pd:Alatomic ratios. Catalyst D comprised a layered sphere with an inner coreof cordierite with a 3 mm diameter, and a 25 micrometer outer layer ofγ-alumina (Al₂O₃). The metals deposited on the outer layer were 0.02 wt% Pd, and 0.33 wt % K on the bulk basis. The theoretical Pd:Al atomic inthe layer is 0.002, and the catalyst was prepared with long evaporationprocedure with acid.

A second catalyst, Catalyst E, comprised the same makeup as catalyst D,except the outer layer was a 50 micrometer outer layer of γ-alumina(Al₂O₃). The theoretical Pd:Al atomic in the layer is 0.001.

A third catalyst, Catalyst F, comprised a layered sphere with an innercore of cordierite with a 3 mm diameter, and a 25 micrometer outer layerof γ-alumina (Al₂O₃). The metals deposited on the outer layer were 0.05wt % Pd, and 0.33 wt % K on the bulk basis. The theoretical Pd:Al atomicin the layer is 0.005, and the catalyst was prepared with longevaporation procedure with acid.

A fourth catalyst, Catalyst G, was a commercially available catalystwith 0.1 wt % Pd on γ-alumina on a 0.1″ diameter sphere (2.54 mm).

The Pd:Al ratio profiles, shown in FIG. 5, for the catalysts were takenwith XPS sputtering. Catalyst D was designed with a 25 micrometer layerto achieve a measured Pd:Al ratio of 0.002. Catalyst E, due to surfaceenrichment has a Pd:Al atomic ratio of 0.002, which is twice itstheoretical value according to the Catalyst E bulk composition. CatalystF has a Pd:Al atomic ratio of 2.5 times the ratio of Catalyst D, due tothe higher Pd loading. Catalyst G has a Pd loading of 1000 wt ppm and isconsidered a state-of-the-art catalyst for this application.

The performance of these four catalysts, along with Catalyst B, iscompared for the selective hydrogenation of MAPD and is shown in FIGS. 6and 7. The feed composition had 1300 wt. ppm MA and 300 wt. ppm PD,65/35 C3/C3=. The reaction conditions were 3550 kPa (500 psig) with ahydrogen to MAPD molar ratio of 1.2. The catalyst bed temperature was40° C. The results shown in FIG. 6 indicate that Catalyst D has the bestactivity among Catalysts D, E, F and G. The propylene recovery is shownas a function of MAPD conversion in FIG. 7. Catalyst D also has the bestselectivity among the Catalysts D, E, F and G with the Pd onlyformulation. Furthermore FIG. 7 shows that Catalyst D has comparableselectivity to the Pd/Cu formulation of Catalyst B. Catalyst F has ahigher Pd loading, but is less active than Catalyst D. This suggeststhat the optimum Pd:Al ratio is below that of Catalyst F at 0.005.Catalyst G, which is a commercial catalyst and has about twice theloading of Catalyst F, has activity drop even more than Catalyst F.

A further test included the sulfur recovery behavior of the catalysts.Sulfur was introduced in the form of H₂S at approximately 3 wt. ppmsulfur in the reactor feed. The H₂S was introduced in the gas phasealong with hydrogen. The gas was mixed with the liquid feed before thereactor inlet as the combined feed. The liquid phase feed comprised 1300wt ppm MA and 300 wt ppm PD. Sulfur was also introduced as organicsulfur via the liquid phase feed. In the liquid phase, the organicsulfur phase used iso-butyl-mercaptan and thiophene with an equivalenttotal sulfur contribution of 1 wt. ppm each in the liquid feed. Theliquid phase feed comprised a 200 wt. ppm MA and a 50 wt. ppm PD. Theresults are shown in FIG. 8 which shows the sulfur recovery behavior.Although all the catalysts showed some loss of activity in the presenceof H₂S, Catalyst D maintained activity during the organic sulfur testsand also recovered its activity better than Catalyst G from the H₂Sphase.

While the invention has been described with what are presentlyconsidered the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but it isintended to cover various modifications and equivalent arrangementsincluded within the scope of the appended claims.

1. A catalyst for selective hydrogenation comprising: a layeredstructure having an inner core comprising an inert material; an outerlayer bonded to the inner core, comprising aluminum oxide and a metaloxide selected from the group consisting of gamma alumina, deltaalumina, eta alumina, theta alumina, silica-alumina, zeolites,nonzeolitic molecular sieves, titania, zirconia, and mixtures thereof; afirst metal deposited on the outer layer, wherein the first metal isselected from a first group consisting an IUPAC Group 8-10 metal, andmixtures thereof; and a second metal deposited on the outer layer,wherein the second metal is selected from a second group consisting ofan IUPAC Group 11-17 metal, and mixtures thereof wherein the atomicratio of the first metal to the aluminum in the outer layer is in aratio between 0.0001 and 0.1, wherein the atomic ratio of the secondmetal to the first metal is less than
 6. 2. The catalyst of claim 1further comprising a third metal deposited on the outer layer, whereinthe third metal comprises a metal selected from the group consisting ofan IUPAC Group 1-2 metal, and mixtures thereof.
 3. The catalyst of claim2 wherein the third metal is selected from the group consisting ofpotassium or lithium.
 4. The catalyst of claim 1 wherein the atomicratio of the first metal to the aluminum in the outer layer is in aratio between 0.001 and 0.005.
 5. The catalyst of claim 1 wherein thefirst metal is palladium or platinum.
 6. The catalyst of claim 1 whereinthe second metal is selected from the group consisting of copper,silver, gold, tin, germanium, lead, and mixtures thereof.
 7. (canceled)8. The catalyst of claim 7 wherein the atomic ratio of the second metalto the first metal is less than 1.5.
 9. The catalyst of claim 1 whereinthe inner core comprises a solid material selected from the groupconsisting of cordierite, mullite, olivine, zirconia, spinel, kyanite,aluminas, silicas, aluminates, silicates, titania, nitrides, carbides,borosilicates, boria, aluminum silicates, magnesia, fosterite, kaolin,kaolinite, montmorillonite, saponite, bentonite, clays that have littleor low acidic activity, gamma alumina, delta alumina, eta alumina, thetaalumina and mixtures thereof.
 10. The catalyst of claim 1 wherein theinner core has an effective diameter from 0.05 mm to 10 mm.
 11. Thecatalyst of claim 1 wherein the outer layer has an effective thicknessbetween 1 micrometers and 200 micrometers.
 12. The catalyst of claim 11wherein the outer layer has an effective thickness between 20 and 70micrometers.
 13. The catalyst of claim 1 wherein the metal oxide is asilica-alumina molecular sieve.
 14. The catalyst of claim 1 wherein themetal oxide is gamma-alumina.
 15. The catalyst of claim 1 wherein themetal oxide is theta-alumina.
 16. The catalyst of claim 1 furthercomprising a modifier metal, wherein the metal is selected from thegroup consisting of an IUPAC Group 6-7 metal and mixtures thereof. 17.The catalyst of claim 16 wherein the modifier metal is selected from thegroup consisting of molybdenum, tungsten, rhenium, and mixtures thereof.18. A catalyst for selective hydrogenation comprising: a layeredstructure having an inner core comprising an inert material; an outerlayer bonded to the inner core, and comprising an alumina; a first metaldeposited on the outer layer, wherein the first metal is palladium; anda second metal deposited on the outer layer, wherein the second metal iscopper; wherein the atomic ratio of the first metal to the aluminum inthe outer layer is in a ratio between 0.001 and 0.005, wherein theatomic ratio of the second metal to the first metal is less than
 6. 19.(canceled)
 20. The catalyst of claim 19 wherein the atomic ratio of thesecond metal to the first metal is less than 1.5.
 21. The catalyst ofclaim 18 wherein the inner core has an effective diameter from 0.05 mmto 10 mm.
 22. The catalyst of claim 18 wherein the outer layer has aneffective thickness between 1 micrometers and 200 micrometers.